1. Field of the Invention
The present invention relates to a surface acoustic wave device for use as a resonator, a band-filter, or other suitable device, and more particularly, to a surface acoustic wave device including electrodes of Al or a metal containing Al as a major component which are formed on an LiTaO3 substrate, and which include a protection layer formed of an SiO2 film.
2. Description of the Related Art
Previously, 36° and 39.5° to 46° rotated Y-cut X-propagation LiTaO3 substrates have been widely used as surface acoustic wave substrates for use in surface acoustic wave devices. For high frequency surface acoustic wave filters including such surface acoustic wave substrates, Al or Al base alloys have been used as major components of the electrode materials. For surface acoustic wave devices of this type, the film thicknesses of interdigital transducers (IDTs), which are normalized by the wavelength λ of a surface acoustic wave, are relatively large, i.e., in the range of about 0.08 to about 0.10.
In such devices, it is well known that an SiO2 film is provided to improve the temperature characteristics and also to protect the electrodes, such as the IDTs, or other suitable electrodes. For example, Japanese Unexamined Patent Application Publication Nos. 2-37815, 8-265088, and 9-186542 disclose surface acoustic wave devices in which an SiO2 film is provided.
Of these surface acoustic wave devices, the surface acoustic wave filter described in Japanese Unexamined Patent Application Publication No. 9-186542 includes reflectors provided on both sides in the surface acoustic wave propagation direction of an area including at least two IDTs. An SiO2 film having a predetermined thickness is arranged so as to cover the IDTs and the reflectors. Japanese Unexamined Patent Application Publication No. 9-186542 discloses that not only the electrodes are protected, but also the band-width is increased when the SiO2 film is provided.
However, problematically, when an SiO2 film is provided in a surface acoustic wave device, the insertion loss is deteriorated due to the addition of the SiO2 film.